This project is concerned with biochemical studies of retina and pigment epithelium with particular emphasis on those biochemical events that may be involved in photoreceptor cell viability in the cat. Cats deprived of dietary taurine develop retinal taurine deficiency which has been associated with photoreceptor cell malfunction and photoreceptor cell death. The cat retina has a capacity to concentrate taurine in vivo against a 1,600 fold gradient, and in vitro studies have shown the presence of a high-affinity uptake mechanism that appears to be associated with the photoreceptor cells. Taurine in vivo is concentrated in the outer nuclear layer, and thin layer chromatography indicates that taurine is not metabolized in situ. In vitro studies of the cat retina have shown that uptake and release of taurine are affected by light.